#include <iostream>
int factorial(int n) 
{
    if (n == 0)
       return 1;
    return n * factorial(n - 1);
}
 
int foo()
{
    return factorial(4); // == (4 * 3 * 2 * 1 * 1) == 24
}

int main()
{
 std::cout << foo();
}
